Conversion of hydrocarbon oils



Filed May 25, 1934 RECEIVER FURNACE 35 FURNACE FURNACE 36 FURNACE 69FURNACE INV TOR KENNETH S TWOOD TTORNEY Patented Nov. 3, 1936 ATET()FFICE CONVERSION OF HYDROCARBON OILS Application May 23, 1934, SerialNo. 727,068

2 Claims.

This invention particularly refers to an improved process for thefractional distillation of hydrocarbon oils of relatively wide boilingrange, accompanied by the pyrolytic conversion of selected fractions ofthe oil employing a plurality of successive conversion stages, each ofwhich is devoted to the separate conversion of selected low-boiling andhigh-boiling fractions of the intermediate products of the precedingstage, the intermediate products of the final cracking stage beingeither Withdrawn, all or in part, from the system or returned, all or inpart, to further conversion in any desired preceding stage of thesystem.

The advantages of selective cracking, i. e. conversion of selectedfractions of oils of different boiling characteristics each underindependently controlled conversion conditions, are now well recognized.It has proven advantageous in proc esses operated primarily for theproduction of 10W-boi1ing products, such as motor fuel of high antiknockvalue, from the standpoint of both the yield and quality of the finallight distillate product. This is generally accounted for by the factthat oils of materially different boiling characteristics requiredifferent cracking conditions for their most advantageous treatment andthat higher yields of the desired products may be obtained from a givenoil of relatively narrow boiling range under the cracking conditions towhich it is best suited when unmixed with any appreciable quantity ofsubstantially lower boiling or higher boiling oils.

In cracking operations employing the recirculation of intermediateconversion products (reflux condensateformed in the fractionator of thesystem) to the heating coil for further conversion the ratio of thequantity of reflux condensate returned to the heating coil to thequantity of raw oil charging stock supplied to the system, when crackingan oil of relatively wide boiling range is normally from 3:1 to 5:1 andin some cases even more. This means that reflux condensate formed byconversion of the charging stock during its initial passage through theheating coil is subjected to further conversion not only with thecharging stock but also with reflux condensates formed by furtherconversion of the previously formed reflux condensate and indicates thatsome portions of the reflux condensate are recycled through the heatingcoil and subjected to further conversion several times while otherportions of the reflux condensate are subjected to further conversiononly once.

I have found that, when a cracking process is divided into severalsuccessive conversion stages, each maintained under independentlycontrolled conversion conditions and each stage, after the first, beingdevoted to the further conversion of intermediate products (refluxcondensate) from 5 the preceding stage, a higher yield and betterquality of product may be obtained. I have applied the term stagecracking to this method of operation and in the present invention, inorder to obtain the advantages of both stage crack- 10 ing and selectedcracking, the charging stock, as well as the intermediate conversionproducts of each cracking stage are separated into selected low-boilingand high-boiling fractions each of which are subjected to independentlycontrolled 5 conversion conditions in the succeeding stage of thecracking operation.

It is, of course, apparent that there is an economic balance between thenumber of different cracking stages which may be employed as well as thedegree of selectivity of the operation (the number of selected fractionsinto which the charging stock and intermediate conversion products ofeach stage are separated) and the improved results obtainable. It is,therefore, not 25 intended to limit the invention to any specific numberof cracking stages or to any specific de-' gree of selectivity and, inthe preferred form of the present invention, the intermediate conversionproducts of the final cracking stage of the process may be removed, allor in part from the system, or may be returned, all or in part, to thatstage of the system employing the conditions most suitable for theirfurther conversion and, particularly, in the latter case, are preferably35 separated into selected low-boiling and highboiling fractions each ofwhich are subjected to independently controlled conversion conditions inthe particular stage to which each is returned.

In one specific embodiment, the invention com- 40 prises subjectinghydrocarbon oil of relatively wide boiling range to fractionaldistillation whereby it is separated into low-boiling, intermediate andhigh-boiling components, separately recovering the low-boiling andhigh-boiling 45 components, separating the intermediate components intoselected low-boiling and high-boiling fractions, subjecting each of saidfractions to independently controlled conversion conditions of elevatedtemperature and superatmospheric 5 pressure, commingling the resultingproducts, separating the commingled materials into lowboiling,intermediate and high-boiling components, separately recovering the lastmentioned low-boiling and high-boiling components, sepa- 55 rating thelast mentioned intermediate components into selected low-boiling andhigh-boiling fractions, subjecting each of the last mentioned selectedfractions to independently controlled conversion conditions of elevatedtemperature and superatmospheric pressure, commingling the resultingproducts, separating the last mentioned commingled materials tolow-boiling, intermediate and high-boiling components, separatelyrecovering the last mentioned low-boiling and highboiling components,separating the last mentioned intermediate components into selectedlow-boiling and high-boiling fractions and subjecting each to furtherconversion in a selected preceding conversion stage of the system.

The accompanying diagrammatic drawing illustrates one specific form ofapparatus in which the process may be practiced. Referring to thedrawing, raw oil charging stock for the process, comprising hydrocarbonoil of any desired type, particularly oils of relatively wide boilingrange and specifically including oil such as crude petroleum containingan appreciable quantity of materials within the boiling range ofgasoline, is supplied through line I and valve 2 to pump 3 by means ofwhich it is fed through line 4, valve 5, heating coil 6, line l andvalve 8 into distilling and fractionating column 9.

Heating coil 6 is located within a furnace ll) of any suitable form bymeans of which sufficient heat is supplied to the charging stock toeffect its substantial subsequent vaporization in column 9. Any desiredpressure ranging from substantially atmospheric to several hundredpounds per sq. in. may be employed in heating coil 6 and, when desired,particularly in case the charging stock is an oil of relatively narrowboiling range the temperature employed within the heating coil may besufficient to efiect its pyrolytic conversion. Preferably, however, incase the charging stock is of relatively wide boiling range only mildconversion temperatures or a temperature below that at which anyappreciable conversion of the charging stock will occur under thepressure conditions prevailing in this zone, are employed therein.

The heated materials supplied, as described, to column 9 are separatedtherein by fractional distillation into low-boiling, intermediate andhighboiling fractions. The high-boiling fractions are allowed toaccumulate within the lower portion of column 9 and, in the case hereillustrated, are withdrawn therefrom through line H and valve I2 tocooling and storage or to any desired further treatment. This materialmay comprise, for example, heavy fuel oil, or, in general high-boilingcomponents of the charging stock or of the conversion products, in caseconversion temperatures are employed in heating coil 6, which it is notdesired to subject to further conversion.

Fractionated vapors of the desired end-boiling point, comprising anylow-boiling components of the charging stock or conversion products, incase cracking conditions are employed in heating coil 6, which it is notdesired to subject to further conversion, such as, for example,materials with in the boiling range of motor fuel, may be withdrawn,together with uncondensable gas, from the upper portion of column 9,through line 13 and valve I4 to be subjected to condensation and coolingin condenser [5. The resulting distillate and gas passes through line l6and valve I! to collection and separation in receiver l8. Uncondensablegas may be released from the receiver through line l9 and valve 20.Distillate may be withdrawn from receiver I8 through line 2! and valve22 to storage or to any desired further treatment.

The intermediate components of the materials supplied to column 9,comprising materials which it is desired to subject to furtherconversion within the system, are separated by fractionation in column 9into selective low-boiling and highboiling fractions. The high-boilingfractions may be withdrawn from any desired intermediate point orplurality of points in column 9, such as, for example, through line 23and valve 24, to pump 25, by means of which they are supplied throughline 26 and valve 21 to conversion in heating coil 28. The low-boilingfractions of the intermediate components from column 9 are separatelywithdrawn from any suitable intermediate point or plurality of points inthe column, for example, through line 29 and valve 33, to pump 3|, bymeans of which they are supplied through line 32 and valve 33 toconversion in heating coil 34.

Heating coils 28 and 34 are located within the respective furnaces 35and 36, each of any desired form, by means of which the respectivehigh-boiling and low-boiling fractions are each subjected toindependently controlled conversion temperatures, preferably underindependently controlled superatmosphcric pressures. The heated productsare discharged from heating coil 28 through line 3'! and valve 38 and,in the case here illustrated, commingle in line 39 with the stream ofheated products discharged from heating coil 34 through line 39 andvalve 49, the commingled materials being discharged into column 4|.

The conversion products supplied to column 4! are separated therein intodesirable low-boiling, selected intermediate and high-boilingcomponents. The latter, comprising residual liquid conversion products,may be withdrawn from the lower portion of the column through line 42and valve 43 to cooling and storage or to any desired further treatment.The desirable low-boiling components are withdrawn as fractionatedvapors of the desired end-boiling point from the upper portion of column4!, together with uncondensable gas, through line 44 and valve 45 to besubjected to condensation and cooling in condenser 46. The resultingdistillate and gas passes through line 41 and valve 48 to collection andseparation in receiver 49. Uncondensable gas may be released from thereceiver through line 50 and valve 5!. Distillate may be withdrawn fromthe receiver through line 52 and Valve 53 to storage or to any desiredfurther treatment. Components of the vapors undergoing fractionation incolumn 4i boiling above the range of the desired final light distillateproduct from this stage of the process are condensed in column 4| asreflux condensate and separated by fractionation into selectedlow-boiling and high-boiling fractions.

The high-boiling fractions of the reflux condensate are withdrawn from asuitable point in column 4| above the point of introduction of the hotconversion products, for example, through line 54 and valve 55, to pump56 by means of which they are supplied through line 51, valve 53 andline 59 to further conversion in heating coil 60. Low-boiling fractionsof the reflux condensate formed in column 4! are withdrawn from anysuitable intermediate point or plurality of points in this zone, forexample, through line GI and valve 62, to pump 63 by means of which they83 and valve 84.

are supplied through line 64, valve 65 and line 66 to further conversionin heating coil 61.

Heating coils Bil and 6'1 are located within the respective furnaces 68and 69, each of any desired form, by means of which the respectivehigh-boiling and low-boiling fractions of the reflux condensate fromcolumn M are each subjected to independently controlled conversionconditions of elevated temperatures and superatmospheric pressures. Thehighly heated products are discharged from heating coil 61 through lineill and valve H, commingling, in the case illustrated, in line H withthe stream of heated products discharged from heating coil 66 throughline 12 and valve T3, the commingled materials being discharged intocolumn M.

Conversion products supplied to column 14, as described, are separatedinto desirable low-boiling, selected intermediate and high-boilingfractions. The latter comprising residual liquid conversion products,may be withdrawn from the lower portion of column l4 through line 15 andvalve 16 to cooling and storage or to any desired further treatment. Thelow-boiling fractions, comprising components of the conversion productsboiling within the range of the desired light distillate product of thisstage of the process, are withdrawn as fractionated vapors from theupper portion of column 14, together with uncondensable gas, throughline H and valve '18 to be subjected to condensation and cooling incondenser l9. The resulting distillate and gas passes through line 853and valve 8! to collection and separation in receiver 82. Uncondensablegas may be released from the receiver through line Distillate may bewithdrawn from receiver 82 through line 85 and valve 86 to storage or toany desired further treatment. Intermediate fractions of the conversionproducts supplied to column M comprising vaporous products boiling abovethe range of the desired final light distillate product of this stage ofthe system are condensed by fractionation in this zone and are separatedinto selected low-boiling and high-boiling fractions.

' High boiling fractions of the reflux condensate from column I l may bewithdrawn from any suitable point in this zone above the point ofintroduction of the hot conversion products, for example, through line8'! and valve 88, to pump 89 by means of which they are fed through line98 and may be returned, all or in part, either through valve 9! and line59 to further conversion in heating coil fill, together with thehighboiling fractions of the reflux condensate from column M, or throughline 92, valve 93 and line 26 to further conversion in heating coil 23,to gether with the high-boiling fractions of the reflux condensate fromcolumn 9.

Low-boiling fractions of the reflux condensate formed in column l4 maybe withdrawn from any suitable intermediate point or plurality of pointsin this zone, for example, through line 94 and valve 95, to pump 96 bymeans of which they are fed through line 91 and may be directed, all orin part, through valve 98 and line 68 to further conversion in heatingcoil 61, together with lowboiling fractions of the reflux condensatefrom column ll, or through line 99, valve l0!) and line 32 to furtherconversion in heating coil 34, together with low-boiling fractions ofthe reflux condensate from column 9.

In a process such as illustratd and above described, the preferred rangeof operating conditions may be approximately as follows; the heatingcoil to which raw oil charging stock for the process is supplied mayutilize an outlet temperature within the range of relatively mildconversion conditions or, may employ a temperature when desired, belowthat at which any appreciable conversion of the oil will occur; thepreferred temperatures ranging, for example, from 600 to 900 F., orthereabouts, with any desired pressure measured at the outlet from theheating coil within the range of substantially atmospheric pressure to300 pounds, or more, per sq. in. The pressure employed in the succeedingdistilling and fractionating column may be substantially equalized orappreciably reduced relative to the pressure employed at the outlet fromthe heating coil. The temperature employed at the outlet from theheating coil to which highboiling fractions of the reflux condensatefrom the first distilling and fractionating column are supplied mayrange, for example, from 800 to 909 F., or thereabouts, preferably witha substantial superatmospheric pressure measured at this point in thesystem of from 100 to 500 pounds, or thereabouts, per sq. in. Thetemperature employed at the outlet from the other heating coil of thisstage of the process, to which low-boiling fractions of the refluxcondensate from the first distilling and fractionating column aresupplied, may range, for example, from 900 to 1000 F.,'or thereabouts,preferably with a superatmospheric pressure at the outlet from theheating coil of from 200 to 800 pounds, or more, per sq. in. Thepressure employed in the succeeding fractionating and distilling columnmay be either substantially equalized with or appreciably reducedrelative to the pressure employed in the preceding heating coilemploying the lowest pressure. The temperature employed for conversionof the high-boiling fractions of the reflux condensate from the seconddistilling and fractionating column, as measured at the outlet from theheating coil may be within the range of 850 to 950 F., preferably with asuperatrnospheric pressure at this point in the system of from 100 to500 pounds, or thereabouts, per sq. in. The temperature employed at theoutlet from the heating coil to which low-boiling fractions of thereflux condensate from the second distilling and fractionating columnare supplied may range, for example, from 950 to 1050 F., preferablywith a superatmospheric pressure of from 200 to 800 pounds, or more, persq. in. The succeeding fractionating and distilling column may utilize apressure either substantially equalized with or somewhat reducedrelative to that employed at the outlet from the preceding heating coilutilizing the lowest pressure. The condensing and collecting equipmentof each stage of the process may utilize pressures substantially thesame or somewhat reduced relative to the pressure employed in thecommunicating distilling and fractionating column.

As a specific example of one of the many possible operations of theprocess of the present invention as it may be practiced in an apparatussuch as illustrated and above described, the charging stock, comprisinga Kansas crude of about 36 A. P. I. gravity, is subjected in the firstheating coil to an outlet conversion temperature of approximately 650 F.at a superatmospheric pressure of about pounds per sq. in. Lowboilingfractions of the straight-run gasoline contained in the crude, boilingup to approximately 350 F. and comprising a little less than 20 percentof the charging stock, are collected as the light distillate productfrom the first distilling and fractionating column and asphaltic residuecomprising approximately 25 percent of the charging stock separatelyrecovered as the bottoms from the first distilling and fractionatingcolumn. The intermediate components of the charging stock are separatedinto fractions boiling above and below approximately 550 F. Thelow-boiling materials are subjected in a separate heating coil to anoutlet conversion temperature of approximately 970 F. at asuperatmospheric pressure of about 800 pounds per sq. in. Thehigh-boiling fractions are subjected in another separate heating coil toan outlet conversion temperature of approximately 920 F. at asuperatmospheric pressure of about 300 pounds per sq. in. The heatedmaterials are commingled and introduced into the second distilling andfractionating column which is operated at a superatmospheric pressure ofabout 150 pounds per sq. in. The light distillate prodnot of this stageof the process comprises motor fuel having an end-boiling point ofapproximately 385 F. and the residual liquid recovered as bottoms fromthe distilling and fractionating column is suitable as fuel. Theintermediate fractions (reflux condensate) are separated into selectedlow-boiling and high-boiling fractions, the former, having a boilingrange of approximately 385 to 550 F., are subjected in a separateheating coil to an outlet conversion temperature of approximately 980 F.at a superatmospheric pressure of about 800 pounds per sq. in. Thehigh-boiling fractions of the reflux condensate are separately subjectedin another separate heating coil to an outlet conversion temperature ofapproximately 950 F. at a superatmospheric pressure of about 350 poundsper sq. in. The two streams of heated products in the last mentionedheating coils are commingled and the commingled materials are introducedinto a separate distilling and fractionating column, The overheaddistillate product from the last mentioned distilling and fractionatingcolumn comprises motor fuel having an end-boiling point of approximately400 F. and the residual liquid withdrawn as bottoms from this zone isalso a good quality fuel oil. The intermediate conversion products(reflux condensate) are separated into selected low-boiling andhigh-boiling fractions boiling respectively above and belowapproximately 550 F. which are returned, respectively, to the lastmentioned high-temperature and lowtemperature heating coils for furtherconversion.

This operation will produce, per barrel of charging stock, approximately58.5 percent of motor fuel, the blended product from all three stages ofthe process (including the straight-run gasoline) having an antiknockvalue equivalent to an octane number of approximately 65 and in additionthere may be produced about 25 percent of asphaltic material and about12 percent of good quality fuel oil, the remainder being chargeableprincipally to uncondensable gas.

I claim as my invention:

1. A hydrocarbon oil conversion process which comprises fractionatingthe charging oil and separating therefrom a relatively light crackingstock and a heavier cracking stock, subjecting said cracking stocks toseparate independently controlled cracking treatments and then combiningresultant conversion products, fractionating the commingled vapors andseparating therefrom a relatively light reflux condensate and a heavierreflux condensate, cracking these condensates independently of eachother and independently of said cracking stocks, subjecting the crackedvapors of said condensates to common fractionation and separating fromthese commingled vapors a relatively light recycle stock and a heavierrecycle stock, retreating said light and heavier recycle stocks togetherwith said light and heavier cracking stocks respectively, and finallycondensing the fractionated vapors.

2. A hydrocarbon oil conversion process which comprises fractionatingthe charging oil and separating therefrom a relatively light crackingstock and a heavier cracking stock, subjecting said cracking stocks toseparate independently controlled cracking treatments and then combiningresultant conversion products, fractionating the commingled vapors andseparating therefrom a relatively light reflux condensate and a heavierreflux condensate, cracking these condensates independently of eachother and independently of said cracking stocks, subjecting the crackedvapors of said condensates to common fractionation and separating fromthese commingled vapors a relatively light recycle stock and a heavierrecycle stock, retreating said light recycle stock in part with saidlight cracking stock and in part with said light reflux condensate,retreating said heavier recycle stock in part with said heavier crackingstock and in part with said heavier reflux condensate, and finallycondensing the fractionated vapors.

KENNETH SWARTWOOD.

